DE1815532A1 - Process for generating cold - Google Patents

Description

LINDE AKTIENGESELLSCHAFT

H GS / 002

η 458 1815532 str./Kp

10/16/1968

Process for generating cold

The previously known methods for generating cold make use of the fact that a compressed gas, its temperature is below the inversion temperature at which relaxation experiences a cooling. This relaxation is either in one Throttle valve or performed in a work-performing device. So it is necessary to have the gas to be cooled on one To compress pressure, which is significantly above that pressure at which the gas or its decomposition products are later available stand. In the case of work-providing relaxation, there is also the fact that an expansion machine is required because of

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its moving parts are not maintenance-free and in the low-temperature part is difficult to access. These disadvantages are particularly significant when there is only a low cooling capacity is required, for example if in a process for low-temperature decomposition only the insulation losses of the system and the exchanger losses are to be covered.

The object of the invention is to provide a method for generating cold, in particular for small cooling capacities per Nnr to create, which requires little energy with little expenditure on equipment.

This object is achieved according to the invention in that two gas streams, the main components of which have very different boiling temperatures under substantially the same pressure which is greater than the highest of the critical pressures the main components to a temperature lower than the highest of the critical temperatures of the main components, cooled and then mixed.

The pressure upstream of the mixing valve only needs to be higher than the pressure required to overcome the pressure drop in this valve than the pressure after mixing. The pressure of the one gas stream expediently therefore exceeds the pressure of the mixture by no more than $ 10.

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The invention is based on the knowledge obtained by evaluating measurements of the Joule -Thomson effect on mixtures that cold can not only be generated by throttle expansion of a gas to a significantly lower pressure, but also by the fact that a gas at a sufficiently high pressure with a mixed with others, that is, while the system pressure remains the same, it is expanded to its partial pressure in the mixture. The only prerequisite for this effect to occur to a significant extent is that the boiling points of the main components (referring to the same pressure) of each of the gas streams to be mixed are sufficiently far apart, ie that the component which is present in the one gas stream in the greatest concentration , boils significantly lower than that component which is present in the other gas stream in the greatest concentration. Preferably, therefore, there is a gas stream mainly of hydrogen or HeIiUm ₅ of the other gas stream mainly consisting of nitrogen, argon, carbon monoxide, methane, ethane or ethylene. Each of the two gas streams may also represent a mixture, so long as the or the other predominantly contains a predominantly ä a plurality of said higher boiling one or more of the lower boiling components mentioned.

The advantage of the method according to the invention is that neither of the two gas streams suffers a significant pressure loss and that there are control valves in the low-temperature part of the system no fixtures with moveable. Sharing needed.

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A particularly preferred field of application of the invention is the production of a hydrogen-nitrogen mixture for Ammonia synthesis tan connection to the Plüssigstickstcff wash. Since the ammonia synthesis is carried out at pressures of the order of 200 at, one strives to reduce the pressure, 'inter dem the hydrogen is generated., in the following cleaning instructions as far as possible. For this reason The liquid detergent wash is also increasingly under increased Pressure carried out. Depending on which of the above-mentioned processes for generating cold is preferred, - are available There are essentially two processes to choose from: In one, the scrubbing nitrogen is liquefied under low pressure. and then with a pump to the washing pressure, the cold losses are demanded covered by work-performing expansion of the synthesis gas or a nitrogen partial flow (see e.g. US-PS J5 312 075) The second possibility is to compress the nitrogen to about 200 atm, cool it down and to the considerably lower one Wash pressure is relaxed, with the nitrogen in the liquid state (see e.g. Linde reports from Technology and Science No. if / 1958 p.27 / 28).

Both processes have those for the respective type of refrigeration typical disadvantages: the first requires liquid pumps and expansion machines in the cryogenic part. At the second, the pressure loss of nitrogen is considerable; this not only requires an increased effort for the system and operation of the compressor, but two different heat

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Exchanger road are provided, namely one for the heat exchange with the high pressure nitrogen and one for the Heat exchange with the raw hydrogen, which is under lower pressure.

Another object of the invention is to provide a method for obtaining ammonia synthesis gas by cooling raw hydrogen and nitrogen in heat exchange with decomposition products, treating the raw hydrogen in a column in countercurrent with liquid nitrogen and admixing cooled nitrogen to the purified gas leaving the column to create the amount required for setting a hydrogen-nitrogen ratio of 3 "s 1, which can be carried out in a particularly simple apparatus with reduced energy consumption at the same time _e

This object is achieved according to the invention in that the raw hydrogen is fed to the low-temperature part with a pressure of at least - 55 at, preferably about 75 at, and that the nitrogen is compressed to a pressure not significantly greater than before entering the low-temperature part the pressure of the purified gas, which is sufficient to mix in the cooled nitrogen. The cold gained in this way is sufficient to cover the cold losses of the system.

LlNDE AKTIENGESELLSCHAFT

Compared to the known processes with work-producing expansion of the synthesis gas or nitrogen, the The advantage is that, with the exception of control valves, there are no moving parts in the low-temperature part and that neither the raw hydrogen nor the nitrogen suffer a significant loss of pressure. A comparison with those with high pressure nitrogen working processes in which the Joule-Thomson effect of nitrogen is used to cover the cold losses, shows that it is no longer necessary to compress the nitrogen to a much higher pressure than the washing pressure, that the gas mixtures produced, apart from the pressure loss of the Tiöftemperaturteils, with the same pressure for Are available with which the raw hydrogen and nitrogen have been introduced into the plant.

The method according to the invention for producing ammonia synthesis gas is preferably carried out at a pressure of not more than 250 atm, in particular not more than 180 atm. At pressures of more than 180 atm a gas phase with 75 $ Hg and 25 # N ₂ only exists above the liquid phase if the temperature at the top of the scrubbing column is below the boiling point of nitrogen at atmospheric pressure, ie the required low temperature at The top of the washing column could only be reached, for example, by nitrogen evaporating under vacuum.

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If the wash column are operated under higher pressures, its head must tempera, door noon be further lowered * The upper Druckgrcmse is ciort ,, where the desired Together "set sung the gas phase only at temperatures too ^ rr-oiohen Vihi ¹ B ₃ which liefffi.no under the fixed point of nitrogen

The · raw hydrogen for 6.Ig, Arsmoniaksjmthsss ltenn c;, ::; - jh pariiil'i.e combustion of llohlem '] £ .ss. $ R3t-ofCQn ersc ^ t tfo-iv · ^ ;, ^ or this required oxygen is im. ο ir: sr LuftsSidcvr ^ iiL - ^ - ilaü © gevicune ^, j

the also for "the FlllssicitJ- ^ ^ iistoffui IAHG - :; ä fi \: ·" · ^il: Setting the gGifünseht-üii H - s !! .-, - T ^ siialtiiisse ^ & s ^o.? : - ^ BFliGh9n nitrogen supplies ο Da BAn ₅ -vi-s bsreits 2X ^; «sSßnt ₅ ": "; y: ibt is, üen pressure the massersfcofferz-r ^ ipisig anziihsiljszi ^ miiB jiu ^ li the oxygen below srhöh. © i : i -S ^ ncl: - i-QÄ ³ sifcr-: o?: -:;. cl-lt we?. ^: usn _r ΐΐκι gaseous oxygen to v © rdiöii ": - G2 _t ., iierae« c'uzr Sii-fysndige machines with a piston thickener final stage are required ^ as sudern are highly explosive »It is therefore generally provided that the liquid oxygen obtained in the air rectification is pumped to the desired final pressure ™

bring it and then warm it up.

The compressed oxygen can only absorb its cold content emit a gas whose heat capacity has a comparable value; the air compressed to only 5-6 at can do this not in stamping. For this reason, the air separation system

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be equipped with a nitrogen cycle, the final pressure of which is to be chosen so high that the compressed cycle nitrogen when exchanging heat with the cold, compressed oxygen, it can absorb its cold. The circulatory pressure must therefore be about as high as the delivery pressure of the oxygen. Through the subsequent relaxation, the circulatory nitrogen supplies in addition, at least part of the cold necessary for air separation.

Usually, the amount of nitrogen required to operate the nitrogen scrubber is not so large that it would be useful to to use a turbo compressor. In those processes of liquid nitrogen scrubbing in which nitrogen is in gaseous form State is compressed, cooled and then released to the washing pressure, the required final pressure of the nitrogen compressor is also significantly above the final pressure of the nitrogen cycle compressor of the air separation plant, so that the nitrogen for liquid nitrogen scrubbing has so far been compressed in high-pressure piston compressors, at least in the last stages had to become.

A further object of the invention is accordingly, in a method for obtaining ammonia synthesis gas from raw hydrogen, in which the nitrogen for the liquid nitrogen scrubbing and for setting the desired H ₂ : Np " ^Ver "

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is taken from an air separation plant, in the oxygen compressed in the liquid state is warmed by heat exchange with compressed circulating nitrogen, to reduce the equipment and energy expenditure for nitrogen compression.

This is done in a particularly advantageous embodiment of the inventive concept in that the to carry out the Plüssignitrogen scrubbing and nitrogen required to set the desired hydrogen-nitrogen ratio from Compresses the circulation compressor of the air separation plant and that a turbo compressor is used as the circulation compressor.

The circulating nitrogen of the air separation plant and the for The nitrogen required for the production of synthesis gas are therefore compressed in the same machine, which makes the building feasible s conditions for turbo compressors are easy to meet. This is possible due to the fact that nitrogen is used for the synthesis gas production in the gaseous state according to the invention no longer at pressures of about 200 at, but only more on the pressure of hydrogen production, provided this is 55 at exceeds, must be compressed to a pressure that is in the same range as the delivery pressure of the Air separators produced oxygen.

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The method according to the invention offers a second possibility, the synthesis gas recovery plant in more advantageous Way to connect with the air separation plant: The peak cold required to start the liquid nitrogen scrubbing is supplied by liquid nitrogen from the air separation plant. Liquid nitrogen is produced from the pressure column of the air separator withdrawn, relaxed to little more than atmospheric pressure and fed to the last heat exchanger, the the raw hydrogen and nitrogen on their way to the liquid nitrogen washing column flow through. The vaporized nitrogen is combined with that from the top of the low pressure column of the The double rectifier extracting nitrogen is passed to the outside via the heat exchanger of the air separation plant.

The apparatus for carrying out the method for producing ammonia synthesis gas according to the invention is characterized through lines for compressed raw hydrogen, slightly more highly compressed nitrogen, synthesis gas and residual gas, through heat exchangers for cooling raw hydrogen and nitrogen in countercurrent to synthesis gas and residual gas, through a nitrogen washing column with a connection point for the cold end of the raw hydrogen line, with an extraction point for residual gas in the sump, which is connected to the cold end of the residual gas line via at least one expansion valve, with a connection point for the cold end of the syngas line im

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Head and with an opening for feeding in nitrogen into the head and through two lines going out from the cold end of the nitrogen line, each of which has an expansion valve with the opening for feeding in nitrogen or nitrogen. are connected to the synthesis gas line leaving the nitrogen washing column.

The method according to the invention will now be explained using three schematic representations, for example.

1, the raw hydrogen enters the plant through line 1 at a pressure of about 7 <3 ata and ambient temperature and is countercurrent to synthesis gas in heat exchangers 3 and 4 together with a partial stream of the nitrogen compressed to 80 ata arriving through the line cooled, while the remaining nitrogen is passed in the heat exchangers 5 and in countercurrent to the relaxed residual gas. The two nitrogen streams are combined and, together with Λ the raw hydrogen, pass through the heat exchangers 7> 8 and 9. In the heat exchanger 7, synthesis gas is the cooling medium, and in the heat exchanger 8, the residual gas is relaxed from the bottom of the nitrogen washing column 10. The heat exchanger 9 is only used when the The system is cooled using liquid nitrogen from a non-system source.

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The raw hydrogen is fed at 11 at a temperature of 85 ° K into the washing column 10, which operates at about 73 ata. A portion of the cooled nitrogen is applied to the top of the column 10 via the expansion valve 12. Since the critical pressure of the hydrogen-nitrogen mixture is significantly higher than the critical pressures of the main components and the column pressure, the nitrogen changes _{to the liquid state when mixed with H 2} and thus forms the scrubbing liquid required to remove the CO and CHh the remaining nitrogen, namely the amount necessary to adjust the ratio of ^ HgJ1Ng., is through the mixing valve 13 to the head of the column 10 with about 83 K ⁰ leaving gereinigten.Gemisch from hydrogen, 10.5 mol. # nitrogen added. It So nitrogen of about 80 atm is combined with the purified hydrogen-nitrogen mixture withdrawn from the nitrogen washing column, the main component of which is hydrogen and which is under the slightly lower pressure of about 73 at, and in this way the nitrogen at essentially unchanged total pressure expanded to a partial pressure of about 18 at. This measure provides the in stationary operation to cover d The amount of cold necessary for exchange and insulation losses, so that liquid pumps and expansion machines as well as compression to a pressure substantially above the delivery pressure can be dispensed with.

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The synthesis gas leaves the plant after it has passed through the heat exchangers 7, 4 and 3 has been warmed by conduit if the hydrogen-nitrogen ratio in the warm synthesis gas does not yet correspond exactly to the required value, the missing amount of nitrogen is added through line 15.

The bottom product of the washing column 10, which consists essentially of nitrogen, CH _2,. and CO exists, is released in valve 16 to the delivery pressure, warmed in heat exchangers 8, 6 and 5 and withdrawn via line 17.

In the method according to Pig. 2 is the inventive idea in the context of the treatment of the exhaust gas of an ammonia synthesis plant applied.

The Sas to be decomposed, consisting of hydrogen, nitrogen, argon and methane, flows through the system through line 20 with a Pressure from 50 - 80 at. It is cooled in the heat exchangers 21 and 22 in countercurrent to the decomposition products to the extent that that all components with the exception of hydrogen condense. The liquid is separated in the separator 2J, into the Column 24 relaxed and rectified there. The liquid in the swamp methane that collects is fed to heat exchanger 21 via line 25; the overhead product, a mixture of nitrogen

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and argon, is broken down in a further column 26 into gaseous nitrogen as the top product and liquid argon as Bottom product, which is heated in the heat exchangers 22 and 21 and given off through line 27.

The nitrogen from the top of the column 2β goes into the refrigeration circuit of the system: It is heated in the heat exchangers 28, 29 and 30 and compressed in the compressor 31 and cooled down again in the heat exchanger j50. Part of the nitrogen is now performing work in the expansion machine 32 relaxed, gives off heat in the coil 33 to the bottom of the column 26 and is finally in the liquid nitrogen container 34 relaxed. The remaining nitrogen is in the heat exchanger 29 cooled, heated in the coil 35 the bottom of the column 24, is thereby liquefied in the heat exchanger 28 cooled further and also relaxed in the liquid nitrogen container 34. From this liquid nitrogen becomes Part as washing liquid applied to the column 26 and the other part evaporated in the line 36 to the head of the Column 24 to cool. The now gaseous nitrogen is together with the evaporated in the container 34 and nitrogen the top product of the column 2o via the heat exchangers 28, 29 and. 30 fed back to the compressor 3I.

The hydrogen escaping from the separator 23 must now

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nor nitrogen can be added in the ratio required for ammonia synthesis gas. For this purpose a corresponding Part of the compressed and cooled in the compressor 31 Nitrogen prior to feeding into container 34 branched off and added through line 37 and mixing valve 38 to the hydrogen. This is how the nitrogen becomes relaxed to its partial pressure without any significant change in the total pressure and through the cold generated thereby Part of the refrigeration requirement of the process is covered. The synthesis gas leaves the plant through line 39

Fig. 3 shows the combination of liquid nitrogen scrubbing according to Fig. 1 with an air separation plant. The same parts are provided with the same reference numbers.

The raw hydrogen is produced by partial combustion of a Hydrocarbon generated at around 95 atm. The oxygen required for this is also to be made available at 95 atm. In order to obtain this and the nitrogen required for the liquid nitrogen scrubbing, 205,000 Hnr / h air to 6 at compressed, fed through line 50 in the illustrated switching phase to the flow path 51 of a reversing exchanger system, cooled in this in countercurrent to decomposition products and dried and freed from COg. Part of the Flow path 5I coming air now passes through line 52 to

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Turbine 53 * is relaxed there to about 1.5 at and then via the heat exchanger 5 * 4 into the upper column of the air rectifier 55 fed. A further amount of air initially flows through the heat exchanger from line 52 and then partly directly via line 57, partly after passing the heat exchanger 58 through line 59 the lower column of the air rectifier 55 operating at about 6 atm. The remaining amount of air is in the flow path of the reversing exchanger system is brought to approximately the condensing temperature and also enters through line 61 the lower column of the air rectifier 55 · oxygen rich Liquid from the sump of the lower column is via line 62, subcooling countercurrent 63 and expansion valve 64 fed to the upper column to be broken down there into pure oxygen and impure nitrogen. The required for this Return fluid is withdrawn from the lower column at 65 and through heat exchanger 63 and expansion valve 66 abandoned on the top pillar. The impure nitrogen withdrawn from the top of the upper column through line 67, I36 676 NmVh, is in the heat exchangers 63 and 58 and then in the reversing exchanger, in the illustrated switching phase in the flow paths 68 and 69, warmed to ambient temperature; it carries away the water and carbon dioxide precipitated from the air in the previous switching phase.

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The liquid oxygen produced in the bottom of the upper column is withdrawn via line 70 and brought to a pressure of 95 atm in the pump 71. In order to be able to warm up this compressed oxygen, a nitrogen cycle is provided: 112,800 NmVh of gaseous nitrogen are drawn off from the lower column through line 82, heated in the heat exchanger 54 against turbine-expanded air and then divided. One part is heated in the unaltered cross-sections 72 and 75 of the reversing exchanger system, the other in the heat exchangers 74 and 75. Both nitrogen partial flows are then compressed together in the compressor 76 to approx. 80 atm. 75 476 Only / h are cooled in the heat exchanger 75 against nitrogen from the lower column and against compressed oxygen and then divided: The first partial flow passes through the heat exchanger 56 * the second partial flow is in the heat exchanger 77 by compressed oxygen and the third partial flow in the heat exchanger 74 the circulating nitrogen from the lower column is cooled. The three sub-streams are then laid together like the valve 78 on the pressure of the lower column and loaded onto them.

The remainder of the nitrogen compressed by the compressor 76 of 37 324 NmVh is the line 2 of the liquid nitrogen scrubbing system fed and there in the related

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rait pig. 1 described manner. The amount of raw hydrogen arriving through line 1 is 109 252 m? / H; 136,400 Nm ^ / h of synthesis gas are withdrawn through line 14, the pressure of which has only decreased insignificantly due to the pressure drop in the liquid nitrogen scrubbing. The residual gas is withdrawn from line 17 in an amount of 10 I76 Nnr / h at a pressure of a little over 1 at.

The cold necessary to start the liquid nitrogen scrubbing is supplied to the heat exchanger 9 in that the lower Air rectifier column 55 at 79 liquid nitrogen taken, expanded in valve 80 to the pressure of the upper column and evaporated in heat exchanger 9. The gaseous one Nitrogen is combined via line 81 with the nitrogen withdrawn from the top of the upper column via line 67.

8 claims
3 sheets of drawings

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Claims (8)

Claims. 1. Jverf ahren for generating cold, characterized in that two gas streams, the main components of which have very different boiling temperatures, under substantially the same pressure, which is greater than the highest of the critical pressures of the main components, to a temperature which is lower than the highest of the critical temperatures of the main components, cooled and then mixed. 2. The method according to claim 1, characterized in that the pressure of one gas stream is the pressure of the mixture by no more than £ 10. 009826/1808 * -2G- LINDEAKTIENGESELLSCHAFT 3. The method according to claim 1 or 2, characterized in that that one of the gas flows' predominantly of hydrogen or helium, the second predominantly of nitrogen, argon, Carbon monoxide, methane, ethane or ethylene. 4. The method according to any one of claims 1 to 3 for obtaining Ammonia synthesis gas by cooling raw hydrogen and nitrogen in heat exchange with decomposition products, Treating the raw hydrogen in a column in countercurrent with liquid nitrogen and admixing the cooled Nitrogen to the purified gas leaving the column in the for setting a hydrogen-nitrogen ratio of 3i1 required amount, thereby identified « draws that the raw hydrogen the low-temperature part with a pressure of at least 55 at, preferably efcwa 75 at, is supplied and that the nitrogen is compressed to a pressure before entering the low-temperature part which is not significantly greater than the pressure of the purified gas, but which is sufficient to make this the cooled one Mix in nitrogen. 5. The method according to claim 4, characterized in that it is at a pressure of not more than 250 at, preferably of no more than 18O at is carried out. 009826/1808 ⁴ -21 - LINDE AKTIENGESELLSCHAFT 6 .. The method according to claim 4 or 5 * wherein the nitrogen comes from an air separation plant in which oxygen compressed in the liquid state is heated by heat exchange with compressed circulating nitrogen, characterized in that the for performing the liquid nitrogen scrubbing and for setting the desired H ₂ : N ₂ ratio, the nitrogen required is compressed by the circulation compressor of the air separation plant and that a turbo compressor is used as the circulation compressor. 7. The method according to any one of claims 4 to 6, characterized in that that the liquid nitrogen of the air separation system required to start the liquid nitrogen scrubbing is removed. 8. Device for performing the method according to claim 4 or 5, characterized by lines for compressed raw hydrogen, slightly more highly compressed nitrogen, synthesis gas and residual gas (1; 2; 1j3; 16), through heat exchangers (5j ^ l 6; 7; 8) for cooling raw hydrogen and nitrogen in countercurrent to synthesis gas and residual gas, through a nitrogen scrubbing column (10) with a connection point (11) for the cold end of the raw hydrogen line (1), with an extraction point for residual gas in the sump, which has at least one ^v 009826/1808 22- LINDE AKTIENGESELLSCHAFT Relief valve (16) with the cold end of the residual gas line (17) is connected, with a connection point for the cold end of the synthesis gas line (14) in the head and with an opening for feeding nitrogen into the head and through two from the cold end of the nitrogen line (2) outgoing lines that have each §in relaxation valve (12; 13) with the opening for feeding in nitrogen or are connected to the synthesis gas line (14) leaving the nitrogen washing column (10). 009826/1808